Pretty sure pistols without safeties don't have shear pins. Striker fired guns (well, besides the Sig 320 apparently) generally don't have fully cocked actions, it's little bit of double action trigger pull. They are partially cocked only. On a properly designed pistol (again looking at you, Sig) the striker cannot fall off the sear. The safeties are 1) trigger safety that prevent pulling the trigger without depressing the trigger safety, and 2) a firing pin block which keep the firing pin from moving forward unless the block is moved out of the way by pulling the trigger. Before the 320 debacle I would have said it's impossible to have a modern pistol go off by itself. 1911's are different tho, some manufacturers went back to the pre-80s design without firing pin blocks, so they may not be drop safe.On Shields with no safety, what keeps the sear pin seated?